The effect of Ru addition upon catalyst characteristics and performance in Fischer-Tropsch synthesis was investigated using a series of differently prepared, Ru-promoted Co/Al2O3 catalysts. Ru promotion facilitated reduction of Co/Al2O3 leading to catalysts with higher reducibilities. Parallel to this effect, the number of reduced metal atoms exposed on the surface increased for the Ru-promoted catalysts. Ru-promoted catalysts showed an increase in CO hydrogenation activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase in the number of metal surface atoms caused the activity enhancement. Isotopic transient kinetic analysis of CO hydrogenation under methanation conditions gave identical results, Catalysts prepared by a co impregnation technique, avoiding chloride salts, appear to be optimal for the production of high-molecular-weight hydrocarbons.